As-cast Al‒Si alloys always face low ductility because of coarse α-Al grains and large lamellar eutectic Si. Although B-containing refiners and Sr modifiers could refine the α-Al grains and eutectic Si respectively, simultaneous addition leads to an invalid effect of Sr because B-containing refiner has a poisoning effect (PE) on Sr modifier in the Al‒10Si‒B‒Sr alloys. The present work achieves both refinement of α-Al grains and modification of Si merely by the addition of 500 ppm La in Al‒10Si‒0.02B‒0.015Sr alloy, which greatly enhances the ductility and tensile strength. Sr‒B interaction in the Al‒10Si‒0.02B‒0.015Sr melt results in a consumption of Sr by forming Sr‒B intermetallic compound. CALPHAD-type calculations reveal that Sr concentration in liquid before eutectic reaction becomes a key parameter to estimate the alloying modification effect. The addition of La forms LaB₆ and thereby releases Sr to protect the Sr modification effect. First-principles calculations illustrate that both Sr and La are beneficial to the formation of twin boundaries in Si particles due to their negative formation energy of twin boundaries. The formed LaB₆ has a semicoherent interface with α-Al with the orientation relationship of [1$\overline{1}$0]_LaB6//[1$\overline{1}$0]_Al and (1$\overline{1}$1)_LaB6//(1$\overline{1}$1)_Al, demonstrating that LaB₆ is an efficient nucleation site for α-Al, which contributes to the refinement of α-Al in the Al‒10Si‒0.05La‒0.02B‒0.015Sr alloy. Our findings reveal the micro-mechanism of refinement during the solidification process and develop an effective and simple way to obtain high-performance Al alloys.

由于粗大的 α-Al 晶粒和大的层状共晶硅，铸态 Al-Si 合金总是面临低延展性。虽然含B细化剂和Sr改性剂可以分别细化α-Al晶粒和共晶Si，但同时添加会导致Sr的无效作用，因为含B细化剂对Al-10Si-中的Sr改性剂具有毒化作用（PE） B-Sr 合金。目前的工作仅通过在 Al-10Si-0.02B-0.015Sr 合金中添加 500 ppm La 就实现了 α-Al 晶粒的细化和 Si 的改性，大大提高了延展性和抗拉强度。Al-10Si-0.02B-0.015Sr 熔体中的 Sr-B 相互作用通过形成 Sr-B 金属间化合物导致 Sr 的消耗。CALPHAD型计算表明，共晶反应前液体中的Sr浓度成为评估合金化改性效果的关键参数。₆从而释放 Sr 以保护 Sr 改性效果。第一性原理计算表明，Sr和La由于双晶界的形成能为负，有利于Si颗粒中双晶界的形成。所形成的LaB ₆与α-Al 具有半共格界面，取向关系为[1$\overline{1}$0] _LaB6 //[1$\overline{1}$0]_铝和 (1$\overline{1}$1) _LaB6 //(1$\overline{1}$1) _Al，表明LaB ₆是α-Al的有效形核位点，有助于细化Al-10Si-0.05La-0.02B-0.015Sr合金中的α-Al。我们的研究结果揭示了凝固过程中细化的微观机制，并开发了一种有效且简单的方法来获得高性能铝合金。